With the development of display technology, the resolution of a display device is required to be higher and higher. The higher the resolution is, the smaller the size of a pixel unit should be, which increases the difficulty in manufacturing the display device. For an organic light-emitting diode display device, a plurality of thin film transistors are provided in each pixel unit. Since the organic light-emitting diode display device has a high resolution, each thin film transistor in the pixel unit has a smaller size, which requires higher manufacturing precision.